Recently, in a blowing device to be incorporated in an electrical equipment such as ventilation device, there is an increasing demand for a blowing device of lower price, higher efficiency, lower noise, smaller pressure loss by duct piping configuration, higher resistance to pressure loss changes due to external wind pressure or clogging of filter, and excellent in controllability so as to ventilate at a constant wind volume by an optimum wind volume depending on an appropriate wind volume depending on the indoor atmosphere.
Conventionally, this type of blowing device is disclosed in, for example, patent literature 1. This blowing device is explained below while referring to FIG. 7.
As shown in FIG. 7, blowing device 10 incorporates centrifugal blower 110a. Centrifugal blower 110a is driven by brushless DC motor 111. Direct-current voltage controller 108 is a step-down chopper circuit for converting a high voltage including ripples after full-wave rectification of a commercial alternating-current power source into a direct-current voltage of 45 V or less. Supply current value controller 122 controls direct-current voltage value changer 114 so that the average current value to inverter circuit 106 to be detected by current detector 121 may be equal to the current value indicated by current value indicator 119, and controls by feedback while varying the output voltage of direct-current voltage controller 108. Wind volume controller 132 changes the current to be supplied in inverter circuit 106 with respect to the reference set value, depending on the output voltage of direct-current voltage controller 108, and indicates to current value indicator 119.
Such conventional blowing device requires a direct-current voltage controller formed of a chopper circuit, and in a blowing device of large output of blowing wind volume, the energy-saving effect may be significantly lowered, and the control circuit is increased in size. Accordingly, in spite of the blowing device of a large output, it is required to adjust the specification easily, such as wind volume-static pressure characteristic and setting of plural wind volumes, without lowering the energy-saving effect.
From the viewpoint of cold draft, when installed in a ventilation device required to reduce the blowing air volume at a constant wind volume, in winter as compared with summer, the blowing wind volume in summer and the blowing wind volume in winter cannot be changed. Therefore, without increasing the required circuit space, it is required to adjust the specification easily, such as wind volume-static pressure characteristic and setting of plural wind volumes, and to control the blowing wind volume depending on the changes of atmospheric temperature.    Patent literature 1: Japanese Patent Unexamined Publication No. 2007-100574